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The camera lies

By Rob Edwards

RELYING on video surveillance to nail criminals may be landing innocent
people behind bars, warn psychologists who have spotted a potential flaw in the
system. About a third of the time, volunteers can’t identify unfamiliar faces on
video stills, they have found.

Vicki Bruce of the University of Stirling and Mike Burton of the University
of Glasgow tested the ability of 230 Open University students to match pictures
of faces grabbed from video with still photographs of ten similar faces. The
faces, which were all young, clean-shaven short-haired Caucasian males, were
pulled from a Home Office database of 200 trainee police officers.

To their surprise, Bruce and Burton found that even in ideal
conditions—using high quality pictures, full-frontal faces and neutral
expressions—only 70 per cent of identifications were correct. When the
face grabbed from video was smiling, the proportion of accurate matches dropped
to 64 per cent. When it was shown at an angle of 30 degrees, the figure was only
61 per cent.

In a second experiment, 60 students at the University of Stirling watched
short high-quality video clips of unknown faces and tried to match them with 10
photographs. Even when they were told that one of the ten photographs matched,
and they could rewind and pause the video as much as they wished, only 79 per
cent of the identifications were accurate.

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However, other experiments showed that when faces caught on poor quality
video were familiar to the student volunteers over 90 per cent of their
identifications were correct. Bruce and Burton will publish their findings later
this year in two American journals, Psychological Science and the
Journal of Experimental Psychology: Applied.

“Although people are very good at identifying faces they know, they are very
bad at comparing faces they don’t know,” says Bruce. “What we are learning is
that two images of the same face can look remarkably different while images of
different faces can look remarkably similar.” She says juries should be warned
about the hazards of making identifications from video pictures.

Britain leads the world in video surveillance, with over a million closed
circuit television (CCTV) cameras recording people’s movements in streets,
shopping centres and offices. Police routinely identify suspects and often
secure convictions with CCTV evidence. Yet, according to a Dispatches
TV programme to be broadcast on Channel Four this week, people may have been
wrongly identified from CCTV pictures and then imprisoned.

Graham Davies, a psychologist at the University of Leicester who advises the
Home Office on visual identification, has also found high error rates in video
identification experiments. This could cause miscarriages of justice, he warns:
“I am very concerned about CCTV because it bestows a kind of spurious scientific
glitz on identification.”